GB1325457A - Photoelectric device for detecting the position of a graduation - Google Patents

Abstract

1325457 Photo-electric position determination DR JOHANNES HEIDENHAIN 6 Aug 1970 [6 Aug 1969] 38057/70 Heading G1A In photo-electric apparatus, for measuring the position of a graduation line or mark, in which. an image of the line is directed towards a photo- ' detector and in which there is inter-posed on the radiation path an oscillating wine or shutter or an oscillating minor or plane parallel block associated with a fixed aperture, there is provided either a switch 3 in the photo-detector circuit or a device changing the polarization of the beam, the detector arrangement being responsive to these charges in polarization, the switch or the device being controlled by the movement of the oscillating element, so that the detector output is directed alternately into two separate channels 9, 10 one operative on the pulse sequence occurring during forward movements of the element and the other on the sequence occurring during return movements, the phase relationship between particular components of the same harmonic frequency in the two pulse sequences being determined as an indication of the required position. As shown, changeover of switch 3 is synchronised with the moments when the element changes direction by the output from pulse shaper 7. The device 8 is an adjustable phase displacer to render this synchronisation exact. The switch 3 thus delivers the detector output alternately into identical channels 9, 10 via lines 4 and 5. The particular harmonic frequency of interest e.g. the sixth is determined by filtering out all except this one in filter 34. A reference harmonic waveform is obtained from the oscillations of the element via frequency multipliers 13, 14 and filter 15. This passes via amplitude and phase adjusters 17, 18, for summation with the detector output at 11. The harmonic waveform on line 12 is applied to adjustable phase displacers 21, 22, shapers 23, 24 to produce on lines 25-28 a four-phase output. The signals are inverted by NAND gates 29-32 and used to switch the amplifier 36 output on to one of lines 37-40 in sequence. The anti-phase signals on lines 37, 39 are summed and then integrated at 19, and on lines 39, 40 summed and then integrated at 20. Devices 19, 20 adjust 17, 18 respectively to establish a fixed phase relationship between the harmonic waveform 12 and that harmonic component in the pulses on line 4. The harmonic waveform on line 12 is compared after pulse shaping at 41 with the correspondingly formed harmonic from circuit 10, in phase comparator 42 to give an indication at 43 of the graduation position.